Tunable magnetron



Patented ug. 30, 1949 Y 2,4so,4 62

Y TNABLE MAGNE'rnoN Howard W. Garbe, Hinsdale, Ill., assignor toWesternl Electric Company, Incorporated, New York, N. Y., acorpcration'of New York Application January 7, 1944, seriaiNo; 517,379

- 1 Claim. v 1

This invention relates to tunable magnetrons and more particularly to amethod of and apparatusl for varying the output frequency of 'amagnetron oscillator. Y

Magnetron oscillators of the type consisting, in their simplest form,.of a two-element tube with a cylindrical plate structure and a co-axialfilament used with a magnetic eld parallel to or nearly parallel to thelament, are Widely used as generators of ultra high frequencyoscillations. In the operation of electronic apparatus employing amagnetron oscillator, it is sometimes desirable to be able to vary thefrequency of the magnetron oscillator, as, for example, where thefrequency employed is jammed by enemy action. While several methods areknown for varying the frequency of magnetron oscillators, they involveex# tensive changes in the tuning of the various elements of theoscillator circuit and cannot be readily employed.

An object of the present invention is to .provide an efiicient andeffective method of and apparatus for readily varying the outputfrequency of a magnetron oscillator.

In accordance with one embodiment of this invention, the frequency of amagnetron oscillator may be switched to another predetermined frequencyor several other predetermined frequencies by moving one or more plugsinto one =or more of the planetary apertures of the magetron anc-de bodyto decrease the volumetric size of the resonant cavity, the plug beingmoved preferably by a loi-'metallic strip to which it is connected andwhichis provided with a remotely controllable heater element.

Other objects and advantages of the present invention will be moreapparent from the following detailed description taken in conjunctionwith the drawings, wherein Fig. 1 is a side elevation, partly insection, showing a magnetron oscillator tube constructed in accordancewith one embodiment of the present invention;

Fig. 2 is a fragmentary, vertical sectional view along the line 2-2 ofFig. 1; and

Fig. 3 is an enlarged vertical sectional view along the line 3-3 of Fig.2.

Referring now to the drawings and particularly to Fig. l thereof, amagnetron oscillator tube is there illustrated comprising a cylindricalanode block I0, which may be made of copper, and which has formedtherein an axially extending cylindrical cathode chamber II in which acylindrical cathode I2 is disposed having a suitable heater elementpositioned therein. Cylindrical recesses I3 and I 4 are formed in theright and left ends, respectively, of the block Ill, as viewed in thisfigure, and the ends' of the cathode I 2 extend into these recesseswhere they are connected to rigid supporting leads I5. The leads I5 arevertically disposed and their lowerk ends extend through tubular glassseals i6 mounted on the lower side of the anode block I0. Suitablecurrent supplying means, not shown, may be connected to these leads toprovide the current required for the cathode heater element.

Radially spaced about the cathode chamber Il are eight planetary axiallyextending cylindricalA apertures I1 which are connected to the center ofthe cathode chamber II by eight radial slots I8. .The cathodechamber,the planetary apertures and the slots cooperatively' form the resonantcavity, the volumetric size of which is one of the factorswhichdetermine the frequency of oscillation of the magnetron. Two smallcircular straps 20 are mounted in suitable circular recesses I9, formedat either'end of the anode block I0 within the recesses I3 and I4, asshown, and are Welded to alternate areas between the planetary aperturesI1, while two other circular straps 2I of somewhat greater size than thestraps 20 are mounted concentrically of the straps 20 and connect thealternate areas between the planetary holes not connected bythe straps20. A pickup loop 22 extends downwardly from an output lead 23, which ismounted on the upper side of the anodev -block I0, into the-upper of theplanetary apertures I ``I,the loop being electrically connected to theoutput lead 23.

End plates 25 are welded to either end of the anode block I0 and theentire tube is sealed against air. After the various parts of the tubehave been assembled and the end plates welded into place, the air in thetube is substantially completely evacuated through a pumping tube 26which is connected to the lower end of the anode block I0 and is spacedbetween the cathode lament leads I6, as shown in Figs. 1 and 2.

'I'he total volumetric size of the resonant cavity formed by the eightplanetary apertures, the slots and the cathode chamber, directly affectsY the frequency of the magnetron oscillator, and a reduction in thetotal volumetric size will proportionately reduce this frequency ofoscillation. By moving a plug 30, of suitable diameter to t closelywithin a planetary aperture, into one of these planetary apertures, itwill be apparent that the volumetric size of the planetary apertures,and therefore of the resonant cavity, will be reduced. It has beenfound,4 in accordance with this in- 3 Vention, that by inserting a plugin one of the planetary apertures, the o-utput frequency of themagnetron oscillator may be materially changed and may be switched fromthe normal operating frequency to a, predetermined other frequencywithout aiecting the efficiency of the unit.

In accordance with one embodiment of this invention, which may. bepracticed with very slight modicationof the magnetronunt, the plug 39may be moved into the end of one of the planetary holes I1 by abi-metallic element 3l which,

may be mounted, as shown in Fig. 3, in the pumpe ing tube 26. A heaterelement 32 is positionedadjacent the high expansive sideV ofi-theloi-metallic element 3l and is providedolvL extend through the base ofthe sealed pumping tube 26 and are lconnected toasuita'ble source 3 8 ofcurrent, such as a battery.` A switch 39 is provided for controlling theactuation of the` heater element 32. A bar 34 is.we1ded to the upper endof thebifmetallic s tripflA andthe upper end of thebar extends into asmall, longitudinally ex. tending aperture35- formedmid-way between twoof theA planetary holes il', as shown in Fig. 2.. An-

integrally formed rod shaped. portion 3 9 which extends to the. right,as shown in Fig. 3, ofthe. plug 30, is slidably positionedin the hole 35and is provided with a notch 3.7.into which the.upper end of the rod3,4'l extends. It will be apparent,

thus, that moving of the rod 34from one side .to 3, the other willcausernovement of the plug 30.

either. into or outE of the planetary hole I'l with which it isassociated. The bi-.metallic strip is.

preferably pre-loadedso that the operating temperature of the magnetrontube will not cause it to move, that is, the additionalheat of theheater element. 32 should be necessary to cause any` movement oftheloi-metallic element 3l.

In the operation of the ,tuning device when it becomes desirable tochange theJ4 frequency of oscillation. of the magnetronytube, theswitch. 39 is closed and current is applied tothe heaterL element 32 tocause the b ifmetalli strip to move the rod attached thereto to theright as, viewed;

ieiFis- 3, This Causesihefplus @reenter the planetary hole l] withwliichit,isassociated.` It'V Wilbe apparent that the device.. couldbemadeContinuously. adjustable by. employing a rheostat.

411V to adjust the current. suppliedl to the. .heater element-ginsteadofthe Switchf. The tuning device could be made remotelycontrollable; by,locating the Switch. 3.9;.-011. theV control: panel 0f.: the apparatus.`with whiehthe magnetroniis. to,

be used.

While it is believed that the foregoing tuning device is the simplestmethod of readily varying the frequency of the magnetron oscillator andwould involve the least modication of the magnetron tube, it wouldinvolve no departure from the spirit or scope of the present inventionto substitute for the heater element and bi-metallic strip, a, solenoidywhich obviously could be remotely controlled, or a, Sylphonv typebellows, either of which could be connected to the plug 30 so, as toimpart the desired movement thereto, and, both of which could beoperated by remotely controllable means.

What is claimed is:

A. variablefrequency magnetron tube including anv anode body having acathode chamber, an aperture therein and a slot leading from saidchamber to said aperture, a tubular pumping seal connected to said anodebody for evacuating the air therefrom, a plug receivable in saidaperture forl varying the volumetric size of the interior of said tube`to alter the frequency of. oscillation of the magnetron, a. bi-metallicstrip mounted` within said tubular pumping seal and having its .V upperend movable upon the application of heat, means. movably connecting theupper end of said bi-metallic strip to saidy plug, means positioned insaid pumping sealfor heating said bi-metallic strip to move said pluginto or out of said aperture, and means extending out of said seal forsupplying electrical current to said heating means.

HOWARD. W. GARBE.

REFERENCES CITED The following references are ofrecord inthe le of this.patent:

UNITEDA STATES PATENTS Number Name DateV 2,079,809;` Kuhle et al.V May11, 1937 2,163,589 Dallenbach et al. June 27, 1939 2,259,690 Hansen etal. Oct. 21, 1941 2,306,860 Black Dec. 29, 1942 2,374,810 Fremlin May 1,1945 2,408,234 Spencer Sept. 24, 1946l 2,408,817 Snow Oct. 8, 19462,414,496 Varian et al. Jan. 21, 1947 2,414,785 Harrison et al. Jan. 21,1947 2,422,465y Bondley June 17, 1947 FOREIGN PATENTS Number CountryDate 509,102 Great Britain July l1, 1939

